7 yr old wakes 4.30/5am - can we shift his body clock?

My DS, aged 7, has always been an early waker. It used to be that he woke around 6am, and slowly he's got used to the fact that we're not much fun till about 7am, and his sister wakes around then, so now he reads till 7, then he wakes everyone else up. I haven't set an alarm once since he was born...

However, I hadn't quite realised that he is now waking much earlier, and almost every day it's around 5am, and often 4.30am. He is bolt awake and full of cheer at that time, but the trouble is, by the evening, he's exhausted by about 6pm.

Now I know you'll all think I should just put him to bed later, but it makes not a second of difference, he's still wide awake by 5am.

The problem is really ours, but we really miss being able to spend time with him in the evening (we both work), and most kids in his class go to bed at more like 8/8.30 - but he's weepy and exhausted by about 7.

He clearly needs about 10 hours sleep, but is there any way of literally shifting his body clock so he goes to sleep an hour later and wakes an hour later?

Any tips gratefully received (apart from the obvious put him to bed later, because we have tried that - although admittedly not over and over again, but he wakes at exactly the same time and then literally cries all day the next day as he's so miserably tired...)

I guess it's a bit mean as he's perfectly happy and very good at filling his 2 hours in the morning pottering about and reading a lot, but still, I'd rather we could rearrange it just a bit. I also think he'd benefit from a bit of time with just us, and no little sister, just to feel like he's the grown up one - as it is, he's often asleep before her!

And also, no, please don't make me get up at 5, I am not good at that hour...

Ah the heating, clicky radiators, I remember changing the time they turned on so many times in the hope it was that, but no... Yes, I bet you're right I'll long for an early wake up as soon as he turns 13! Hope yours gets better soon. Or gets into reading! That helped a lot.